1. Field of the Invention
The present invention relates to a liquid crystal display device and driving method thereof, and more particularly, to a liquid crystal display device capable of removing afterimages from a screen when a power source is turned-off, and a driving method thereof.
2. Discussion of the Related Art
Generally, a liquid crystal display device can display images by controlling light transmittance of liquid crystal with an electric field applied thereto. For this, the liquid crystal display device is comprised of a liquid crystal panel including a plurality of pixels arranged in a matrix configuration; and a driving circuit for driving the liquid crystal panel.
The liquid crystal panel includes a thin film transistor formed adjacent to each crossing of gate and data lines, and the pixel connected to the thin film transistor.
The thin film transistor is provided with a gate electrode and a source electrode, wherein the gate electrode is connected to any one of gate lines in a horizontal line unit, and the source electrode is connected to any one of data lines in a vertical line unit. The thin film transistor supplies a data signal from the data line to the pixel in response to a gate-driving pulse from the gate line.
The pixel is comprised of a pixel electrode connected to a drain electrode of the thin film transistor, and a common electrode facing the pixel electrode with the liquid crystal interposed therebetween. The pixel drives the liquid crystal in response to the data signal supplied to the pixel electrode, thereby controlling the light transmittance.
Hereinafter, a related art liquid crystal display device will be described with reference to the accompanying drawings.
FIG. 1 is an equivalent circuit diagram illustrating one pixel of a liquid crystal display device according to the related art.
As shown in FIG. 1, each of pixels included in a liquid crystal display device is defined by gate and data lines GL and DL crossing each other. Each pixel is provided with a thin film transistor TFT and a pixel electrode. In more detail, the thin film transistor TFT is formed adjacent to each crossing of the gate and data lines GL and DL. The thin film transistor TFT is provided with a gate terminal connected to the gate line GL, a source terminal connected to the data line DL, and a drain terminal connected to the pixel electrode.
The liquid crystal display device includes two facing glass substrate bonded to each other, and a liquid crystal layer formed between the two glass substrates. FIG. 1 shows one pixel formed on the lower glass substrate of liquid crystal display device, that is, first substrate including a thin film transistor array.
Although not shown, the upper glass substrate is provided in opposite to the lower glass substrate, that is, second substrate including R, G and B color filter layers and a common electrode 150 to display images. At this time, the pixel electrode on the first substrate is provided in opposite to the common electrode 150 on the second substrate with the liquid crystal layer interposed therebetween. The light transmittance of liquid crystal layer is controlled based on an intensity of electric field generated between the pixel electrode and the common electrode. In this case, the facing pixel and common electrodes 160 and 150 with the liquid crystal layer interposed therebetween function as a liquid crystal capacitor Clc using the liquid crystal layer as a dielectric.
Each pixel electrode included in each pixel is partially overlapped with the gate line G1 for driving the adjacent pixel. At this time, the pixel electrode and gate line GL facing each other function as an auxiliary capacitor Cst using an insulator as a dielectric. Generally, as described above, the pixel electrode included in each of the pixels overlaps with the gate line GL of the adjacent pixel, which is referred to as a previous gate structure.
An operation of the pixel will be explained as follows.
First, when the thin film transistor TFT is turned-on according to a gate high-voltage applied to the gate line GL, the liquid crystal capacitor Clc and the auxiliary capacitor Cst receives the voltage from the data line DL through the source and drain terminals of the thin film transistor TFT turned-on, thereby representing gray scales. Then, a gate low-voltage is applied to the gate line GL, so that the thin film transistor TFT is turned-off. According as the thin film transistor TFT is turned-off by the gate low-voltage, the display of gray scale is stably maintained by the electric charges charged to the auxiliary capacitor Cst during one frame.
When a power is turned-off from the liquid crystal display device, afterimages occur for a short period of time. Specifically, electric charges slowly disappear from pixel cells when the power is turned off causing the afterimages to appear on the display panel of the liquid crystal display device.